The objective of this research project is to understand the transport of amino acids into mammation cells in molecular terms. For these studies we are using Chinese Hamster Ovary cells grown in culture and Ehrlich Ascites Tumor Cells grown in mice. Using the tissue culture cells we are selecting transport mutants by two genetic approaches. One approach involves a tritium suicide technique and the second approach involves toxic analog resistance. We are characterizing the transport systems of several mutants obtained from the above selections. The regulation of amino acid transport is being examined in the tissue culture cells. We find that both sodium-dependent and sodium independent uptake is regulated during amino acid starvation conditions. In a separate approach membranes are prepared from Ehrlich Ascites cells for purification and reconstitution of the transport systems. The membrane proteins are solubilized using detergents and the purified proteins are reconstituted into phospholipid vesicles which carry out active transport of amino acids.